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<tr class="t-nv"><td colspan="5"> <a href="explicit.html" title="cpp/language/explicit"><tt>explicit</tt></a> <span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
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<tr class="t-nv-h2"><td colspan="5"> Special member functions</td></tr>
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<tr class="t-nv"><td colspan="5"> <a href="move_constructor.html" title="cpp/language/move constructor"> Move constructor</a> <span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
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<tr class="t-nv"><td colspan="5"> <a href="as_operator.html" title="cpp/language/as operator" class="mw-redirect"> Copy assignment</a></td></tr>
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<tr class="t-nv"><td colspan="5"> <a href="template_specialization.html" title="cpp/language/template specialization"> Template specialization</a></td></tr>   
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<tr class="t-nv-h1"><td colspan="5"> Miscellaneous </td></tr>
<tr class="t-nv-col-table"><td><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"> <a href="asm.html" title="cpp/language/asm"> Inline assembly</a></td></tr>
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<tr class="t-nv"><td colspan="5"> <a href="history.html" title="cpp/language/history"> History of C++</a></td></tr>
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</div><div></div></div></div></div><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="declarations.html" title="cpp/language/declarations"> Declarations</a><div class="t-navbar-menu"><div><div style="display:inline-block">
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<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="typedef.html" title="cpp/language/typedef"><span class="t-lines"><span>typedef</span></span></a></div></div></td></tr>
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<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="consteval.html" title="cpp/language/consteval"><span class="t-lines"><span>consteval</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="constinit.html" title="cpp/language/constinit"><span class="t-lines"><span>constinit</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="storage_duration.html" title="cpp/language/storage duration"> storage class specifiers</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <strong class="selflink"> translation-unit-local</strong> <span class="t-mark-rev t-since-cxx20">(C++20)</span></td></tr>
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<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="enum_class.html" title="cpp/language/enum"><span class="t-lines"><span>enum</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="decltype.html" title="cpp/language/decltype"><span class="t-lines"><span>decltype</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
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<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="alignas.html" title="cpp/language/alignas"><span class="t-lines"><span>alignas</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="cv.html" title="cpp/language/cv"><span class="t-lines"><span>const</span><span>volatile</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="elaborated_type_specifier.html" title="cpp/language/elaborated type specifier"> elaborated type specifier</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="attributes.html" title="cpp/language/attributes"> attributes </a><span class="t-mark-rev t-since-cxx11">(C++11)</span> </td></tr>
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<tr class="t-nv-h2"><td colspan="5"> Declarators </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="reference.html" title="cpp/language/reference"> reference </a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="pointer.html" title="cpp/language/pointer"> pointer </a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="array.html" title="cpp/language/array"> array </a> </td></tr>
<tr class="t-nv-h2"><td colspan="5"> Block declarations </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="declarations.html" title="cpp/language/declarations"> simple-declaration</a> </td></tr>
<tr class="t-nv"><td colspan="5"> →<a href="structured_binding.html" title="cpp/language/structured binding"> structured binding declaration</a> <span class="t-mark-rev t-since-cxx17">(C++17)</span> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="type_alias.html" title="cpp/language/type alias"> <code>alias</code> declaration</a><span class="t-mark-rev t-since-cxx11">(C++11)</span> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="namespace_alias.html" title="cpp/language/namespace alias"> namespace alias definition </a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="using_declaration.html" title="cpp/language/using declaration"> using-declaration</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="namespace.html#Using-directives" title="cpp/language/namespace"> using-directive</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="static_assert.html" title="cpp/language/static assert"> <code>static_assert</code> declaration</a> <span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="asm.html" title="cpp/language/asm"> asm-declaration</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="enum_class.html" title="cpp/language/enum"> opaque enum declaration</a><span class="t-mark-rev t-since-cxx11">(C++11)</span> </td></tr>
<tr class="t-nv-h2"><td colspan="5"> Other declarations </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="namespace.html" title="cpp/language/namespace"> namespace definition</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="function.html" title="cpp/language/function"> function declaration</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="class_template.html" title="cpp/language/class template"> class template declaration</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="function_template.html" title="cpp/language/function template"> function template declaration</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="class_template.html#Explicit_instantiation" title="cpp/language/class template"> explicit template instantiation</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="template_specialization.html" title="cpp/language/template specialization"> explicit template specialization</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="language_linkage.html" title="cpp/language/language linkage"> linkage specification</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="declarations.html" title="cpp/language/declarations"> attribute declaration</a> <span class="t-mark-rev t-since-cxx11">(C++11)</span> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="declarations.html" title="cpp/language/declarations"> empty declaration</a> </td></tr>
</table></div></td></tr>
</table></div>
</div><div></div></div></div></div><div class="t-navbar-sep"> </div></div>
<p>Translation-unit-local (TU-local) entities are introduced to prevent entities that are supposed to be local (not used in any other translation unit) being exposed and used in other translation units.
</p><p>An example from <a rel="nofollow" class="external text" href="https://vector-of-bool.github.io/2019/03/31/modules-2.html">Understanding C++ Modules: Part 2</a> illustrates the problem of not constraining exposures:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co1">// Module unit without TU-local constraints</span>
export module Foo<span class="sy4">;</span>
 
import <span class="sy1">&lt;</span>iostream<span class="sy1">&gt;</span><span class="sy4">;</span>
 
<span class="kw1">namespace</span> <span class="br0">{</span>
   <span class="kw1">class</span> LolWatchThis <span class="br0">{</span>        <span class="co1">// internal linkage, cannot be exported</span>
       <span class="kw4">static</span> <span class="kw4">void</span> say_hello<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
           <a href="../io/cout.html"><span class="kw1762">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">"Hello, everyone!<span class="es1">\n</span>"</span><span class="sy4">;</span>
       <span class="br0">}</span>
   <span class="br0">}</span><span class="sy4">;</span>
<span class="br0">}</span>
 
export LolWatchThis lolwut<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <span class="co1">// LolWatchThis is exposed as return type</span>
    <span class="kw1">return</span> LolWatchThis<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co1">// main.cpp</span>
import Foo<span class="sy4">;</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
    <span class="kw4">auto</span> evil <span class="sy1">=</span> lolwut<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>        <span class="co1">// 'evil' has type of 'LolWatchThis'</span>
    decltype<span class="br0">(</span>evil<span class="br0">)</span><span class="sy4">::</span><span class="me2">say_hello</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// definition of 'LolWatchThis' is not internal anymore</span>
<span class="br0">}</span></pre></div></div>
<h3><span class="mw-headline" id="TU-local_entities">TU-local entities</span></h3>
<p>An entity is <i>TU-local</i> if it is
</p>
<ol><li> a type, function, variable, or template that
<ol><li> has a name with <a href="storage_duration.html#internal_linkage" title="cpp/language/storage duration">internal linkage</a>, or
</li><li> does not have a name with linkage and is declared, or introduced by a <a href="lambda.html" title="cpp/language/lambda">lambda expression</a>, within the definition of a TU-local entity,
</li></ol>
</li><li> a type with no name that is defined outside a <a href="class.html" title="cpp/language/class">class-specifier</a>, function body, or initializer or is introduced by a defining-type-specifier (type-specifier, class-specifier or enum-specifier) that is used to declare only TU-local entities,
</li><li> a specialization of a TU-local template,
</li><li> a specialization of a template with any TU-local template argument, or
</li><li> a specialization of a template whose (possibly instantiated) declaration is an exposure (defined below).
</li></ol>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co1">// TU-local entities with internal linkage</span>
<span class="kw1">namespace</span> <span class="br0">{</span> <span class="co1">// all names declared in unnamed namespace have internal linkage</span>
    <span class="kw4">int</span> tul_var <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>                          <span class="co1">// TU-local variable</span>
    <span class="kw4">int</span> tul_func<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> <span class="nu0">1</span><span class="sy4">;</span> <span class="br0">}</span>              <span class="co1">// TU-local function</span>
    <span class="kw1">struct</span> tul_type <span class="br0">{</span> <span class="kw4">int</span> mem<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>             <span class="co1">// TU-local (class) type</span>
<span class="br0">}</span>
<span class="kw1">template</span><span class="sy1">&lt;</span><span class="kw1">typename</span> T<span class="sy1">&gt;</span>
<span class="kw4">static</span> <span class="kw4">int</span> tul_func_temp<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> <span class="nu0">1</span><span class="sy4">;</span> <span class="br0">}</span>      <span class="co1">// TU-local template</span>
 
<span class="co1">// TU-local template specialization</span>
<span class="kw1">template</span><span class="sy1">&lt;&gt;</span>
<span class="kw4">static</span> <span class="kw4">int</span> tul_func_temp<span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy1">&gt;</span><span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> <span class="nu0">3</span><span class="sy4">;</span> <span class="br0">}</span> <span class="co1">// TU-local specialization</span>
 
<span class="co1">// template specialization with TU-local template argument</span>
<span class="kw1">template</span> <span class="sy1">&lt;&gt;</span> <span class="kw1">struct</span> <a href="../utility/hash.html"><span class="kw1127">std::<span class="me2">hash</span></span></a><span class="sy1">&lt;</span>tul_type<span class="sy1">&gt;</span> <span class="br0">{</span>      <span class="co1">// TU-local specialization</span>
    <a href="../types/size_t.html"><span class="kw106">std::<span class="me2">size_t</span></span></a> operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span><span class="kw4">const</span> tul_type<span class="sy3">&amp;</span> t<span class="br0">)</span> <span class="kw4">const</span> <span class="br0">{</span> <span class="kw1">return</span> 4u<span class="sy4">;</span> <span class="br0">}</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div></div>
<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style=""><tr><td class="mbox-empty-cell"></td><td class="mbox-text" style="">This section is incomplete<br>Reason: missing examples of rules #1.2, #2 and #5 </td></tr></table>
<p>A value or object is <i>TU-local</i> if either
</p>
<ol><li> it is, or is a pointer to, a TU-local function or the object associated with a TU-local variable, or
</li><li> it is an object of class or array type and any of its <a href="objects.html#Subobjects" title="cpp/language/object">subobjects</a> or any of the objects or functions to which its non-static data members of reference type refer is TU-local and is <a href="constant_expression.html#Usable_in_constant_expressions" title="cpp/language/constant expression">usable in constant expressions</a>.
</li></ol>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw4">static</span> <span class="kw4">int</span> tul_var <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>             <span class="co1">// TU-local variable</span>
<span class="kw4">static</span> <span class="kw4">int</span> tul_func<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> <span class="nu0">1</span><span class="sy4">;</span> <span class="br0">}</span> <span class="co1">// TU-local function</span>
 
<span class="kw4">int</span><span class="sy2">*</span> tul_var_ptr <span class="sy1">=</span> <span class="sy3">&amp;</span>tul_var<span class="sy4">;</span>        <span class="co1">// TU-local: pointer to TU-local variable</span>
<span class="kw4">int</span> <span class="br0">(</span><span class="sy2">*</span> tul_func_ptr<span class="br0">)</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">=</span> <span class="sy3">&amp;</span>tul_func<span class="sy4">;</span> <span class="co1">// TU-local: pointer to TU-local function</span>
 
<span class="kw4">constexpr</span> <span class="kw4">static</span> <span class="kw4">int</span> tul_const <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span> <span class="co1">// TU-local variable usable in constant expressions</span>
<span class="kw4">int</span> tul_arr<span class="br0">[</span><span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span> tul_const <span class="br0">}</span><span class="sy4">;</span>      <span class="co1">// TU-local: array of constexpr TU-local object </span>
<span class="kw1">struct</span> tul_class <span class="br0">{</span> <span class="kw4">int</span> mem<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
tul_class tul_obj<span class="br0">{</span>tul_const<span class="br0">}</span><span class="sy4">;</span>       <span class="co1">// TU-local: has member constexpr TU-local object</span></pre></div></div>
<h3><span class="mw-headline" id="Exposures">Exposures</span></h3>
<p>A declaration D <i>names</i> an entity E if
</p>
<ol><li> D contains a lambda expression whose closure type is E,
</li><li> E is not a function or function template and D contains an id-expression, type-specifier, nested-name-specifier, template-name, or concept-name denoting E, or
</li><li> E is a function or function template and D contains an expression that names E or an id-expression that refers to a set of overloads that contains E.
</li></ol>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co1">// lambda naming</span>
<span class="kw4">auto</span> x <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span> <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// names decltype(x)</span>
 
<span class="co1">// non-function (template) naming</span>
<span class="kw4">int</span> y1 <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>                      <span class="co1">// names y1 (id-expression)</span>
<span class="kw1">struct</span> y2 <span class="br0">{</span> <span class="kw4">int</span> mem<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
y2 y2_obj<span class="br0">{</span><span class="nu0">1</span><span class="br0">}</span><span class="sy4">;</span>                    <span class="co1">// names y2 (type-specifier)</span>
<span class="kw1">struct</span> y3 <span class="br0">{</span> <span class="kw4">int</span> mem_func<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">int</span> y3<span class="sy4">::</span><span class="me2">mem_func</span><span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> <span class="nu0">0</span><span class="sy4">;</span> <span class="br0">}</span> <span class="co1">// names y3 (nested-name-specifier)</span>
<span class="kw1">template</span><span class="sy1">&lt;</span><span class="kw1">typename</span> T<span class="sy1">&gt;</span> <span class="kw4">int</span> y4 <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>
<span class="kw4">int</span> var <span class="sy1">=</span> y4<span class="sy1">&lt;</span>y2<span class="sy1">&gt;</span><span class="sy4">;</span>                <span class="co1">// names y4 (template-name)</span>
<span class="kw1">template</span><span class="sy1">&lt;</span><span class="kw1">typename</span> T<span class="sy1">&gt;</span> concept y5 <span class="sy1">=</span> <span class="kw2">true</span><span class="sy4">;</span>
<span class="kw1">template</span><span class="sy1">&lt;</span><span class="kw1">typename</span> T<span class="sy1">&gt;</span> <span class="kw4">void</span> func<span class="br0">(</span>T<span class="sy3">&amp;&amp;</span><span class="br0">)</span> requires y5<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy4">;</span> <span class="co1">// names y5 (concept-name)</span>
 
<span class="co1">// function (template) naming</span>
<span class="kw4">int</span> z1<span class="br0">(</span><span class="kw4">int</span> arg<span class="br0">)</span>      <span class="br0">{</span> <a href="../io/cout.html"><span class="kw1762">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">"no overload"</span><span class="sy4">;</span> <span class="kw1">return</span> <span class="nu0">0</span><span class="sy4">;</span> <span class="br0">}</span>
<span class="kw4">int</span> z2<span class="br0">(</span><span class="kw4">int</span> arg<span class="br0">)</span>      <span class="br0">{</span> <a href="../io/cout.html"><span class="kw1762">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">"overload 1"</span><span class="sy4">;</span>  <span class="kw1">return</span> <span class="nu0">1</span><span class="sy4">;</span> <span class="br0">}</span>
<span class="kw4">int</span> z2<span class="br0">(</span><span class="kw4">double</span> arg<span class="br0">)</span>   <span class="br0">{</span> <a href="../io/cout.html"><span class="kw1762">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">"overload 2"</span><span class="sy4">;</span>  <span class="kw1">return</span> <span class="nu0">2</span><span class="sy4">;</span> <span class="br0">}</span>
 
<span class="kw4">int</span> val1 <span class="sy1">=</span> z1<span class="br0">(</span><span class="nu0">0</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// names z1</span>
<span class="kw4">int</span> val2 <span class="sy1">=</span> z2<span class="br0">(</span><span class="nu0">0</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// names z2 ( int z2(int) )</span></pre></div></div>
<p>A declaration is an <i>exposure</i> if it either names a TU-local entity, ignoring
</p>
<ol><li> the function-body for a non-inline function or function template (but not the deduced return type for a (possibly instantiated) definition of a function with a declared return type that uses a <a href="auto.html" title="cpp/language/auto">placeholder type</a>),
</li><li> the initializer for a variable or variable template (but not the variable’s type),
</li><li>friend declarations in a class definition, and
</li><li> any reference to a non-volatile const object or reference with internal or no linkage initialized with a constant expression that is not an <a href="definition.html#ODR-use" title="cpp/language/definition">odr-use </a>,
</li></ol>
<p>or defines a constexpr variable initialized to a TU-local value.
</p>
<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style=""><tr><td class="mbox-empty-cell"></td><td class="mbox-text" style="">This section is incomplete<br>Reason: missing examples for exposures </td></tr></table>
<h3><span class="mw-headline" id="TU-local_constraints">TU-local constraints</span></h3>
<p>If a (possibly instantiated) <a href="declarations.html" title="cpp/language/declarations">declaration</a> of, or a <a href="deduction_guide.html#Deduction_for_class_templates" title="cpp/language/class template argument deduction">deduction guide</a> for, a non-TU-local entity in a <a href="modules.html" title="cpp/language/modules">module interface unit</a> (outside the private-module-fragment, if any) or module partition is an exposure, the program is ill-formed. Such a declaration in any other context is deprecated.
</p><p>If a declaration that appears in one translation unit names a TU-local entity declared in another translation unit that is not a header unit, the program is ill-formed. A declaration instantiated for a template specialization appears at the point of instantiation of the specialization.
</p>
<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style=""><tr><td class="mbox-empty-cell"></td><td class="mbox-text" style="">This section is incomplete<br>Reason: missing examples for constraints </td></tr></table>
<h3><span class="mw-headline" id="Example">Example</span></h3>
<p>Translation unit #1:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1">export module A<span class="sy4">;</span>
<span class="kw4">static</span> <span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span>
<span class="kw1">inline</span> <span class="kw4">void</span> it<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> f<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span>         <span class="co1">// error: is an exposure of f</span>
<span class="kw4">static</span> <span class="kw1">inline</span> <span class="kw4">void</span> its<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> f<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span> <span class="co1">// OK</span>
<span class="kw1">template</span><span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy1">&gt;</span> <span class="kw4">void</span> g<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> its<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span> <span class="co1">// OK</span>
<span class="kw1">template</span> <span class="kw4">void</span> g<span class="sy1">&lt;</span><span class="nu0">0</span><span class="sy1">&gt;</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
 
decltype<span class="br0">(</span>f<span class="br0">)</span> <span class="sy2">*</span>fp<span class="sy4">;</span>                             <span class="co1">// error: f (though not its type) is TU-local</span>
<span class="kw4">auto</span> <span class="sy3">&amp;</span>fr <span class="sy1">=</span> f<span class="sy4">;</span>                                <span class="co1">// OK</span>
<span class="kw4">constexpr</span> <span class="kw4">auto</span> <span class="sy3">&amp;</span>fr2 <span class="sy1">=</span> fr<span class="sy4">;</span>                    <span class="co1">// error: is an exposure of f</span>
<span class="kw4">constexpr</span> <span class="kw4">static</span> <span class="kw4">auto</span> fp2 <span class="sy1">=</span> fr<span class="sy4">;</span>              <span class="co1">// OK</span>
<span class="kw1">struct</span> S <span class="br0">{</span> <span class="kw4">void</span> <span class="br0">(</span><span class="sy3">&amp;</span>ref<span class="br0">)</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span> s<span class="br0">{</span>f<span class="br0">}</span><span class="sy4">;</span>            <span class="co1">// OK: value is TU-local</span>
<span class="kw4">constexpr</span> <span class="kw4">extern</span> <span class="kw1">struct</span> W <span class="br0">{</span> S <span class="sy3">&amp;</span>s<span class="sy4">;</span> <span class="br0">}</span> wrap<span class="br0">{</span>s<span class="br0">}</span><span class="sy4">;</span> <span class="co1">// OK: value is not TU-local</span>
 
<span class="kw4">static</span> <span class="kw4">auto</span> x <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">{</span>f<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// OK</span>
<span class="kw4">auto</span> x2 <span class="sy1">=</span> x<span class="sy4">;</span>              <span class="co1">// error: the closure type is TU-local</span>
<span class="kw4">int</span> y <span class="sy1">=</span> <span class="br0">(</span><span class="br0">[</span><span class="br0">]</span><span class="br0">{</span>f<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span><span class="br0">}</span><span class="br0">(</span><span class="br0">)</span>,<span class="nu0">0</span><span class="br0">)</span><span class="sy4">;</span>   <span class="co1">// error: the closure type is not TU-local</span>
<span class="kw4">int</span> y2 <span class="sy1">=</span> <span class="br0">(</span>x,<span class="nu0">0</span><span class="br0">)</span><span class="sy4">;</span>           <span class="co1">// OK</span>
 
<span class="kw1">namespace</span> N <span class="br0">{</span>
    <span class="kw1">struct</span> A <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
    <span class="kw4">void</span> adl<span class="br0">(</span>A<span class="br0">)</span><span class="sy4">;</span>
    <span class="kw4">static</span> <span class="kw4">void</span> adl<span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span>
<span class="kw4">void</span> adl<span class="br0">(</span><span class="kw4">double</span><span class="br0">)</span><span class="sy4">;</span>
 
<span class="kw1">inline</span> <span class="kw4">void</span> h<span class="br0">(</span><span class="kw4">auto</span> x<span class="br0">)</span> <span class="br0">{</span> adl<span class="br0">(</span>x<span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span> <span class="co1">// OK, but a specialization might be an exposure</span></pre></div></div>
<p>Translation unit #2:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1">module A<span class="sy4">;</span>
<span class="kw4">void</span> other<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
    g<span class="sy1">&lt;</span><span class="nu0">0</span><span class="sy1">&gt;</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>                  <span class="co1">// OK: specialization is explicitly instantiated</span>
    g<span class="sy1">&lt;</span><span class="nu0">1</span><span class="sy1">&gt;</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>                  <span class="co1">// error: instantiation uses TU-local its</span>
    h<span class="br0">(</span>N<span class="sy4">::</span><span class="me2">A</span><span class="br0">{</span><span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>               <span class="co1">// error: overload set contains TU-local N::adl(int)</span>
    h<span class="br0">(</span><span class="nu0">0</span><span class="br0">)</span><span class="sy4">;</span>                    <span class="co1">// OK: calls adl(double)</span>
    adl<span class="br0">(</span>N<span class="sy4">::</span><span class="me2">A</span><span class="br0">{</span><span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>             <span class="co1">// OK; N::adl(int) not found, calls N::adl(N::A)</span>
    fr<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>                    <span class="co1">// OK: calls f</span>
    <span class="kw4">constexpr</span> <span class="kw4">auto</span> ptr <span class="sy1">=</span> fr<span class="sy4">;</span> <span class="co1">// error: fr is not usable in constant expressions here</span>
<span class="br0">}</span></pre></div></div>
<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style=""><tr><td class="mbox-empty-cell"></td><td class="mbox-text" style="">This section is incomplete<br>Reason: examples are too complex, need better arrangement </td></tr></table>

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